Robert Fitzroy

Barometer and Weather Guide Robert Fitzroy

Book Excerptarly--but does not show the temperature of mercury within exactly. It does so however near enough for ordinary practical purposes--provided that no sun, nor fire, nor lamp heat is allowed to act on the instrument partially. The mercury in the cistern and tube being affected by cold or heat, makes it advisable to consider this when endeavouring to foretell coming weather by the length of the column.* * *Briefly, the barometer shows weight or pressure of the air; the thermometer--heat and cold, or temperature; and the wet thermometer, compared with a dry one, the degree of moisture or dampness.[10]It should be remembered that the state of the air foretells, rather than shows present weather (an invaluable fact too often overlooked); that the longer the time between the signs and the change foretold by them, the longer such altered weather will last; and, on the contrary, the less the time between a warning and a change, the shorter will be the continuance of such foretold